Coupled shear wall structures are recognised as one of the most efficient lateral load resisting systems. To achieve a desirable performance for such a system, coupling beams connecting to the shear walls are usually subjected to a high shear stress, and are designed with a short span and relatively deep depth. However, the shear limitation of concrete and the brittle behaviour of normal reinforced coupling beams, when subjected to seismic load, are the key drivers in seeking new practical solutions, which can increase the shear strength and the seismic capacity of coupling beams. Encasing a vertical steel plate as shear reinforcement into the traditional reinforced concrete coupling beam is therefore considered as an effective way to improve the seismic performance and enhance the shea...[ Read more ]

Coupled shear wall structures are recognised as one of the most efficient lateral load resisting systems. To achieve a desirable performance for such a system, coupling beams connecting to the shear walls are usually subjected to a high shear stress, and are designed with a short span and relatively deep depth. However, the shear limitation of concrete and the brittle behaviour of normal reinforced coupling beams, when subjected to seismic load, are the key drivers in seeking new practical solutions, which can increase the shear strength and the seismic capacity of coupling beams. Encasing a vertical steel plate as shear reinforcement into the traditional reinforced concrete coupling beam is therefore considered as an effective way to improve the seismic performance and enhance the shear strength.

In this thesis, an experimental programme and analytical model development on the shear capacity of steel-plate encased concrete coupling beams are presented. An experimental investigation is first conducted to study the shear strength and structural performance of steel-plate encased concrete coupling beams under both monotonic and reversed-cyclic loads. In the test programme, a new test rig was designed and constructed, with a unique rail and conveyor belt system, to simulate the coupling beam action under lateral load and, at the same time, to accommodate specimens with different span lengths in a rapid and easy manner.

A total of eleven large-scale coupling beam specimens were fabricated, in which nine were constructed with encased steel plates while the other two were conventionally reinforced designed as control specimens. Within the eleven test specimens, four were monotonically loaded while the rests were reversed cyclically loaded. The influences of steel plate ratio, stirrup ratio and span-to-effective depth ratio on the composite coupling beams are discussed. The test results show that the shear strengths attained by all the steel-plate encased concrete coupling beam specimens are much greater than the shear stress limits given in the current codes of practice. In addition, the energy dissipation capacity of the concrete coupling beam can be greatly enhanced by the encased steel plates. The encouraging test results reveal the feasibility of using the steel-plate encased concrete coupling beams in general practice.

A comprehensive database of the test results of steel-plate encased concrete coupling beams is first established herein. The database includes the available experimental data of 41 reinforced concrete coupling beams embedded with vertical steel plates tested by the author and other researchers. The available data in the database was then used to evaluate the effectiveness and accuracy of the common design provisions in Japan, Mainland China, Hong Kong, the United Kingdom, Europe, Canada and the United States, on the strength prediction of the steel-plate encased concrete coupling beams. A comparison showed that the shear contributions from all components, including the steel plate, stirrups and reinforced concrete, should be considered in determining the shear capacity of the composite coupling beams. Among the ten different design approaches, EC4 (2004), JGJ138 (2001) and YB9082 (2006) give better strength prediction with the mean and COV of the strength ratios about 1.03 and 25% respectively.

An analytical model known as Modified Softened Strut-and-tie Model is proposed to predict the shear strength of reinforced concrete coupling beams with encased vertical steel plates. The proposed model is derived mainly based on the softened strut-and-tie model and strip model. The shear resistance of the composite beam is contributed by two shear resisting mechanisms, which are diagonal and vertical ones. The shear strengths predicted by the proposed model show good agreement with the available experimental data. The proposed method provides a rational and effective means for predicting the shear strength of the steel-plate encased concrete coupling beams.